For new installations of Ubuntu I would first try this to get the latest updates
sudo apt-get dist-upgrade
For more info on this see https://askubuntu.com/questions/81585/what-is-dist-upgrade-and-why-does-it-upgrade-more-than-upgrade
That should solve it but if not, add the repository from these guys https://launchpad.net/~git-core/+archive/ppa
sudo add-apt-repository ppa:git-core/ppa
sudo apt-get update
sudo apt-get install git
This way you don’t have to build it, etc.